Detection apparatus, detection method, and computer readable medium

ABSTRACT

Easily detecting cavitation to occur in a pump. A detection apparatus, a detection method, and a program are provided. The detection apparatus includes: a discharge pressure acquiring unit to acquire discharge pressure data indicating discharge pressure of a pump; and a detector to detect occurrence of cavitation in the pump based on a fluctuation amount of a time waveform of the discharge pressure data during a target detection period. The detector may have: a fluctuation amount calculator to calculate the fluctuation amount of the discharge pressure data during the target detection period; and a determining unit to determine, in response to the calculated fluctuation amount becoming the reference fluctuation amount or more, that cavitation has occurred in the pump.

The contents of the following Japanese patent application areincorporated herein by reference.

NO. 2017-211094 filed in JP on Oct. 31, 2017.

BACKGROUND 1. Technical Field

The present invention relates to a detection apparatus, a detectionmethod, and a program.

2. Related Art

Cavitation may occur to a pump that sucks and discharges liquid due tothe liquid evaporating. Conventionally, a technique to detect occurrenceof such cavitation has been known, in which frequency analysis isperformed on discharge pressure of the pump (refer to Patent Document 1,for example).

Patent Document 1: Japanese Patent Application Publication No.S64-45975.

However, according to the technique in Patent Document 1, an arithmeticprocessing of the frequency analysis can be a large burden. For example,in a case of a plant including numerous pumps, i.e., from hundreds tothousands or more pumps, it is possible that cavitation is treated foreach pump. Thus, a technique to efficiently detect cavitation byperforming less arithmetic processing is desired.

SUMMARY

A first aspect of the present invention provides a detection apparatus,a detection method, and a program. The detection apparatus includes: adischarge pressure acquiring unit to acquire discharge pressure dataindicating discharge pressure of a pump; and a detector to detectoccurrence of cavitation in the pump based on a fluctuation amount of atime waveform of the discharge pressure data during a target detectionperiod.

A second aspect of the present invention provides a detection apparatus,a detection method, and a program. The detection apparatus includes: asuction pressure acquiring unit to acquire suction pressure dataindicating suction pressure of a pump; a discharge pressure acquiringunit to acquire discharge pressure data indicating discharge pressure ofthe pump; and a detector to detect whether cavitation is occurring inthe pump based on the discharge pressure data in response to the suctionpressure data becoming a threshold value or less.

A third aspect of the present invention provides a detection apparatus,a detection method, and a program. The detection apparatus includes: adischarge pressure acquiring unit to acquire discharge pressure dataindicating discharge pressure of a pump; and a detector to detectoccurrence of cavitation in the pump based on difference between thedischarge pressure data during a target detection period and thedischarge pressure data before the target detection period.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary configuration of a plant 10 to which adetection apparatus 100 according to the present embodiment is provided.

FIG. 2 illustrates an example of suction pressure data and dischargepressure data acquired by the detection apparatus 100 according to thepresent embodiment.

FIG. 3 illustrates an exemplary configuration of the detection apparatus100 according to the present embodiment.

FIG. 4 illustrates an exemplary operation flow of the detectionapparatus 100 according to the present embodiment.

FIG. 5 illustrates one example of a fluctuation amount of dischargepressure data calculated by a fluctuation amount calculator 160according to the present embodiment.

FIG. 6 illustrates a modification example of the detection apparatus 100according to the present embodiment.

FIG. 7 illustrates an exemplary configuration of a computer 1200 inwhich a plurality of aspects of the present invention may be embodied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the present invention will be described with reference toembodiments of the invention. However, the following embodiments shallnot be construed as limiting the claimed invention. Also, not allcombinations of features described in the embodiments are essential formeans to solve problems provided by aspects of the invention.

FIG. 1 illustrates an exemplary configuration of a plant 10 to which adetection apparatus 100 according to the present embodiment is provided.The plant 10 is a system to control equipment or the like whilesupplying liquid to the equipment or the like by a pump. The plant 10may be at least a part of a plant facility, machinery, a productionapparatus, power generating apparatus, or the like. The plant 10includes equipment 20, a liquid source 30, a pump 40, a suction pressuregauge 50, a discharge pressure gauge 60, and a control system 70. Notethat, at least some of the equipment 20, the liquid source 30, the pump40, the suction pressure gauge 50, the discharge pressure gauge 60, anda detection apparatus 100 which are included in the plant 10 may beplural.

The equipment 20 is subject to control by the plant 10. The equipment 20may be at least a part for plant equipment, machinery, a productionapparatus, power generating apparatus, a storage apparatus, or the like.The equipment 20 may include an apparatus supplied with liquid such aswater, oil, fuel, coolant, or chemicals in order to perform processingoperation using the liquid. The equipment 20 may include a plurality ofapparatuses.

The liquid source 30 stores or supplies the liquid supplied to theequipment 20. The liquid source 30 may be a tank or the like to preserveand store the liquid, and may also maintain pressure of the liquid. Theliquid source 30 may also be a well, an oil well, or the like, which isprovided in a region where a resource such as groundwater or oil fieldis accumulated or reserved. The liquid source 30 may also be a river, apond, a lake, a dam, or the like. The liquid source 30 may also be atank to store liquid supplied by another pump. The liquid source 30 mayalso be a pipe connected to a tank or the like.

The pump 40 supplies the equipment 20 with the liquid of the liquidsource 30. The pump 40 connects between the liquid source 30 and theequipment 20 using a valve, pipe, or the like. FIG. 1 illustrates anexample of a moving direction of liquid inside the pipe with an arrowfrom the liquid source 30 to the equipment 20. The pump 40 may be avolute pump having a rotor in a vane shape (an impeller) or the like.Also, the pump 40 may be a diffuser pump, a cascade pump, an axial flowpump, a mixed flow pump, a cross flow pump, or the like. A plurality ofpumps 40 may be arranged in the plant 10.

The suction pressure gauge 50 is provided between the liquid source 30and the pump 40 and measures suction pressure of the pump 40. Thedischarge pressure gauge 60 is provided between the equipment 20 and thepump 40 and measures discharge pressure of the pump 40. Each of thesuction pressure gauge 50 and the discharge pressure gauge 60 is, forexample, a differential pressure flow meter, a pressure transmitter, orthe like. The suction pressure gauge 50 and the discharge pressure gauge60 may serve as sensors to detect operation of the pump 40. A suctionpressure gauge 50 and a discharge pressure gauge 60 may be provided toeach pump 40. FIG. 1 illustrates an example in which the plant 10 isprovided with one liquid source 30, one pump 40, one suction pressuregauge 50, and one discharge pressure gauge 60. Note that, at least oneof the suction pressure gauge 50 and the discharge pressure gauge 60 maybe used to control the plant 10.

The control system 70 controls a part or the whole of the equipment 20,the pump 40, and the like based on a measurement result of a measuringinstrument such as a sensor provided in a plant. Also, the controlsystem 70 may control a valve provided in a pipe or the like, which isprovided in a plant. For example, the control system 70 controls and/ormonitors operation of the equipment 20, the pump 40, the valve, and thelike based on measurement data obtained by measuring the operation ofthe equipment 20, and measurement data for pressure, temperature, a flowrate, storage capacity, or the like of fluid of liquid etc. that istreated in the plant 10.

The control system 70 is connected to the equipment 20 or the like viawireless and/or wired communication equipment, and may be arranged at aposition away from the equipment 20 or the like. The control system 70may be constructed as an automatic operation system and/or a maintenancesystem such as a DCS (Distributed Control system) and a SCADA(Supervisory Control And Data Acquisition) system. In this case, thecontrol system 70 may exchange control data and measurement data witheach unit at a frequency of approximately several Hz to several kHz.

It is desirable that the above-mentioned plant 10 can perform control,maintenance, management, or the like of the equipment 20 as well as thepump 40. For example, cavitation or the like may occur to the pump 40and may cause noise, and in some cases, it results in degradation and/orbreakage of the pump 40. It is desirable for the plant 10 to be able toperform control, maintenance, management, or the like in order tosuppress as much occurrence of such unstable operation as possible bymonitoring the operation of the pump 40.

It is known to detect cavitation of the pump 40 in order to monitor theoperation of such pump 40 by: performing numerical processing such asthe Fourier transform on the discharge pressure data acquired from thedischarge pressure gauge 60; and detecting abnormality on a frequencyaxis. However, it is difficult to detect the abnormality on thefrequency axis unless the unstable operation of the pump 40 progressesto the state in which an obvious fluctuation characteristic of a certainfrequency or a certain frequency band occurs to the discharge pressuredata. That is, temporal difference occurs from the occurrence ofcavitation to the detection of the cavitation, which makes it difficultto deal with the cavitation in some cases.

Also, such plant 10 illustrated in FIG. 1 can be a large-scale controlsystem including from hundreds to thousands or more of pumps 40. Thus,providing one processing circuit to perform numerical processing foreach pump 40 causes high cost. Furthermore, since the plant 10communicates with each unit at a frequency of approximately several Hzto several kHz, it is difficult to perform accumulation of data,numerical processing, analysis of a result, or the like at high speed.Hence, it is desired for such plant 10 to detect cavitation in real timewhile preventing increase in cost, and further to predict occurrence ofcavitation.

Therefore, the detection apparatus 100 is provided to such plant 10 todetect cavitation in real time based on temporal fluctuation ofdischarge pressure data. The detection apparatus 100 is configured to beapplicable to an existing plant 10 or the like, and can detectcavitation by acquiring the discharge pressure data or the like. Notethat, the detection apparatus 100 may be included in the control system70. Also, the detection apparatus 100 may be included in a measuringinstrument such as a sensor provided in the plant 10. FIG. 1 illustratesan example in which the detection apparatus 100 is included in thecontrol system 70. First, suction pressure data and discharge pressuredata acquired by the detection apparatus 100 will be described.

FIG. 2 illustrates an example of suction pressure data and dischargepressure data acquired by the detection apparatus 100 according to thepresent embodiment. In FIG. 2, the horizontal axes represent the timeand vertical axes represent the suction pressure and the dischargepressure respectively. FIG. 2 is an example to show change in thesuction pressure data and the discharge pressure data, each of whichcorrespond to approximately the same lapse of time, by showing eachmeasurement data in approximately the same time scale. Note that, thesuction pressure data is an example of a measurement result of thesuction pressure gauge 50, and the discharge pressure data is an exampleof a measurement result of the discharge pressure gauge 60.

Along with the operation of the pump 40, the suction pressure data mayshow pressure lower than the atmospheric pressure (negative pressure).FIG. 2 shows an example in which the suction pressure data graduallydecreases and shows pressure lower than the atmospheric pressure fromtime t₀ onwards. Accordingly, if the suction pressure becomes lower thanthe atmospheric pressure, cavitation may occur due to pressure of liquidsupplied from the pump 40 to the equipment 20 being equal to or lowerthan saturated steam pressure and the liquid evaporating.

Note that, as shown in FIG. 2, if a noise component is superimposed onthe suction pressure data, the suction pressure data may show pressurelower than the atmospheric pressure before time t₀. Therefore, it isdesirable that the detection apparatus 100 performs filtering processingon the suction pressure data such as averaging, smoothing, noiseremoving, and/or high frequency removal. Also, the suction pressuregauge 50 and the discharge pressure gauge 60 may supply data on whichsuch filtering processing has been performed.

The discharge pressure data gradually decreases corresponding to thegradual decrease of the suction pressure data. FIG. 2 shows an examplein which the gradual decrease in the suction pressure data continueswith the lapse of time, and unstable fluctuation occurs to the dischargepressure data from approximately time t_(n) onwards. Note that, withrespect to the discharge pressure data from time t_(n) onwards, unstablefluctuation is occurring and causing the discharge pressure data tooscillate, and an amplitude value is gradually increasing. Yet thedischarge pressure data is still in a state in which obvious oscillationof a certain frequency or a certain frequency band is not occurring.That is, for example, even if the Fourier transform is performed on thedischarge pressure data in period T, i.e., from time t_(n) to timet_(n)+T, amplitude strength of a certain frequency band may not be thefrequency characteristic that is different compared with a amplitudestrength of another band. Thus, robustness is also required in thedetection apparatus 100.

Hence, if the discharge pressure data is converted to a frequency axis,cavitation cannot be detected until an obvious frequency signal occurswith the time further preceding the time range shown in FIG. 2. Thedetection apparatus 100 according to the present embodiment can detectoccurrence of cavitation in the time range illustrated in FIG. 2 basedon such time waveforms shown in FIG. 2. Such detection apparatus 100will be described next.

FIG. 3 illustrates an exemplary configuration of the detection apparatus100 according to the present embodiment. FIG. 3 illustrates an exemplaryconfiguration of detection apparatus 100 that detects cavitationoccurring in the pump 40 based on suction pressure data and dischargepressure data. Note that, each of the suction pressure gauge 50, thedischarge pressure gauge 60, and the control system 70 may be connectedto the detection apparatus 100 via wired or wireless connection or thelike. The detection apparatus 100 may be connected to them via a networkor the like. The detection apparatus 100 includes a discharge pressureacquiring unit 110, a suction pressure acquiring unit 120, and adetector 130.

The discharge pressure acquiring unit 110 acquires discharge pressuredata indicating the discharge pressure of the pump 40. The dischargepressure acquiring unit 110 may be connected to the discharge pressuregauge 60 and may receive the discharge pressure data from the dischargepressure gauge 60. Also, if the discharge pressure data is stored in anexternal database or the like, the discharge pressure acquiring unit 110may access the database or the like to acquire the discharge pressuredata. Additionally, the discharge pressure acquiring unit 110 mayacquire the discharge pressure data from the control system 70. Thedischarge pressure acquiring unit 110 supplies the detector 130 with theacquired discharge pressure data.

The suction pressure acquiring unit 120 acquires the suction pressuredata indicating suction pressure of the pump 40. The suction pressureacquiring unit 120 may be connected to the suction pressure gauge 50 andmay receive the suction pressure data from the suction pressure gauge50. Also, if the suction pressure data is stored in a database or thelike, the suction pressure acquiring unit 120 may access the database orthe like to acquire the suction pressure data. Additionally, the suctionpressure acquiring unit 120 may acquire the suction pressure data fromthe control system 70. The suction pressure acquiring unit 120 suppliesthe detector 130 with the acquired suction pressure data.

In response to the suction pressure data becoming a threshold value orless, the detector 130 detects whether cavitation is occurring in thepump 40 based on the discharge pressure data. The detector 130 detectsthe occurrence of cavitation in the pump 40 based on, for example, afluctuation amount of a time waveform of discharge pressure data duringa target detection period. The detector 130 has a storage unit 140, acomparator 150, a fluctuation amount calculator 160, and a determiningunit 170.

The storage unit 140 stores the suction pressure data and the dischargepressure data. Also, the storage unit 140 may be able to store dataprocessed by the detection apparatus 100. The storage unit 140 may storeeach of intermediate data, a calculated result, a parameter, and thelike. The intermediate data is calculated (or utilized) by the detectionapparatus 100 in a process of generating a detection result. Also, inresponse to a request from each unit in the detection apparatus 100, thestorage unit 140 may supply the stored data to the requesting unit. Forexample, in response to a request from the comparator 150, the storageunit 140 supplies the comparator 150 with the stored suction pressuredata.

The comparator 150 compares the suction pressure data with thepredetermined threshold value. For example, the threshold value may be apressure data value corresponding to the atmospheric pressure. Inresponse to the suction pressure data becoming the threshold value orless, the comparator 150 notifies the fluctuation amount calculator 160of the comparison result. That is, the comparator 150 may notify thefluctuation amount calculator 160 about the suction pressure datachanging from being a positive pressure value to a negative pressurevalue.

The fluctuation amount calculator 160 calculates a fluctuation amount ofthe discharge pressure data during the target detection period. Forexample, in response to the notification from the comparator 150, thefluctuation amount calculator 160 reads out the discharge pressure datafrom the storage unit 140 and calculates a fluctuation amount of thedischarge pressure data. The fluctuation amount calculator 160 may setreference pressure data and may calculate the fluctuation amount of thedischarge pressure data from the difference between the referencepressure data and the discharge pressure data. Here, the fluctuationamount calculator 160 uses, for example, the discharge pressure dataacquired by the discharge pressure acquiring unit 110 before the targetdetection period as the reference pressure data. The fluctuation amountcalculator 160 supplies the determining unit 170 with the calculatedfluctuation amount.

The determining unit 170 determines, in response to a fluctuation amountcalculated by the fluctuation amount calculator 160 becoming thereference fluctuation amount or more, that cavitation has occurred inthe pump 40. In response to determining the occurrence of cavitation,the determining unit 170 notifies the control system 70 of thedetermination result.

As described above, the detection apparatus 100 according to the presentembodiment detects occurrence of cavitation based on the fluctuationamount of the discharge pressure data. More specific operation of suchdetection apparatus 100 will be described next.

FIG. 4 illustrates an exemplary operation flow of the detectionapparatus 100 according to the present embodiment. The detectionapparatus 100 performs the operation flow illustrated in FIG. 4 todetect occurrence of cavitation.

First, the detection apparatus 100 acquires discharge pressure data andsuction pressure data (S410). That is, the discharge pressure acquiringunit 110 acquires the discharge pressure data and the suction pressureacquiring unit 120 acquires the suction pressure data. The pressure dataacquired by each of the discharge pressure acquiring unit 110 and thesuction pressure acquiring unit 120 may be stored in the storage unit140. The discharge pressure acquiring unit 110 may acquire pressure dataevery time the discharge pressure gauge 60 performs sampling on thepressure data, and the suction pressure acquiring unit 120 may acquirepressure data every time the suction pressure gauge 50 performs samplingon the pressure data. Instead of this, they may collectively acquire thepressure data every time a predetermined number of times of sampling hasbeen performed.

Next, the comparator 150 compares the suction pressure data with athreshold value (S420). For example, if the suction pressure dataexceeds the threshold value (No at S420), the comparator 150 determinesthat a tendency of cavitation is not detected. In this case, thedetection apparatus 100 returns to S410 and acquires discharge pressuredata and suction pressure data to be sampled next.

Note that, if the suction pressure acquiring unit 120 acquires the nextsuction pressure data and stores it in the storage unit 140, theprevious suction pressure data may be erased. In this case, the suctionpressure acquiring unit 120 may overwrite the previously acquiredsuction pressure data stored in the storage unit 140 with the suctionpressure data acquired next.

Also, the discharge pressure acquiring unit 110 may erase dischargepressure data before the predetermined period T. For example, if thenext discharge pressure data is acquired at t_(k+1), the dischargepressure acquiring unit 110 erases discharge pressure data before timet_(k)−T. In this case, the discharge pressure acquiring unit 110 mayoverwrite the discharge pressure data before time t_(k)−T, which isstored in the storage unit 140, with discharge pressure data acquirednext at time t_(k+1). Accordingly, if pressure data is acquired at timet_(k), the storage unit 140 at least stores the suction pressure dataand the discharge pressure data acquired at time t_(k) and the dischargepressure data acquired from time t_(k)−T, which is back in time fromtime t_(k) by a period T, to time t_(k).

The discharge pressure acquiring unit 110, the suction pressureacquiring unit 120, and the comparator 150 repeat acquiring the pressuredata and comparing the suction pressure data with the threshold valueuntil the suction pressure data becomes the threshold value or less.Then, if the suction pressure data becomes the threshold value or less(Yes at S420), the comparator 150 determines that a tendency ofcavitation is starting to appear, and notifies the fluctuation amountcalculator 160 of the comparison result. Here, an example in which thethreshold value is a pressure data value corresponding to theatmospheric pressure, and the comparator 150 notifies the fluctuationamount calculator 160 about the suction pressure data becoming thethreshold value or less at time t₀ as shown in FIG. 2 is described.

Next, the fluctuation amount calculator 160 sets reference pressure data(S430). Here, time t₀−T is back in time from the time t₀ by a period T.For example, the fluctuation amount calculator 160 reads out thedischarge pressure data acquired from the storage unit 140 from timet₀−T to time t₀ and sets the discharge pressure data as referencepressure data. That is, the fluctuation amount calculator 160 uses asthe reference pressure data the data including the discharge pressuredata acquired corresponding to a timing t₀ at which the suction pressuredata is changed from being a value exceeding the threshold value to thethreshold value or less. In the present example, an example in which thefluctuation amount calculator 160 uses as reference pressure data thedischarge pressure data acquired from timing t₀−T to the timing t₀ isdescribed. The timing t₀−T is back in time from a predetermined period Tby the timing t₀.

The fluctuation amount calculator 160 may store the reference pressuredata that has been set in the storage unit 140. Note that, if previousreference pressure data has been stored in the storage unit 140, thefluctuation amount calculator 160 may overwrite it with the newestreference pressure data that has been set.

Next, the detection apparatus 100 acquires discharge pressure data andsuction pressure data at next sampling time (S440). That is, thedischarge pressure acquiring unit 110 acquires the discharge pressuredata and the suction pressure acquiring unit 120 acquires the suctionpressure data. Note that, if it is immediately after time t₀ elapses,the discharge pressure acquiring unit 110 and the suction pressureacquiring unit 120 may continue acquiring the pressure data until aperiod T elapses, i.e., until time t₀+T.

Next, the comparator 150 compares the suction pressure data with athreshold value (S450). If the comparison result shows that the suctionpressure data exceeds the threshold value (Yes at S450), the detectionapparatus 100 may determine that a tendency of cavitation hasdisappeared and a normal operation state has been restored, and returnto S410. In this case, the comparator 150 may erase information aboutthe reference pressure data from the storage unit 140.

Note that, it is desirable that the threshold value used for comparisonby the comparator 150 at S450 is different from the threshold value usedat S420. For example, if the threshold value used at S420 is a firstthreshold value, a second threshold value used at S450 is larger thanthe first threshold value by a predetermined value. That is, in order toreduce effect of noise or the like that is superimposed on the suctionpressure data, the comparator 150 may perform comparison havinghysteresis. For example, the second threshold value is obtained byadding acceptable magnitude of noise or the like to the first thresholdvalue.

If the suction pressure data is the threshold value or less (No atS450), the comparator 150 may determine that the tendency of cavitationis continuing and notify the fluctuation amount calculator 160 of thisfact.

Next, the fluctuation amount calculator 160 calculates a fluctuationamount of discharge pressure data (S460). The fluctuation amountcalculator 160 sets as a target detection period a period from timingt₂−T to timing t₂. This t₂ is the latest detection timing of thedischarge pressure data acquired by the discharge pressure acquiringunit 110 at S440, and this timing t₂−T is back in time from the timingt₂ by a predetermined period T. Note that, if the discharge pressureacquiring unit 110 continues acquiring the pressure data until timet₀+T, the fluctuation amount calculator 160 may set the target detectionperiod as a period from time t₀ to time t₀+T.

Then, the fluctuation amount calculator 160 calculates as a fluctuationamount difference between reference pressure data and discharge pressuredata during the target detection period. Accordingly, the fluctuationamount calculator 160 may calculate as a fluctuation amount differencebetween discharge pressure data during the target detection period andreference pressure data in a time length T having equal length as thetarget detection period. For example, the fluctuation amount calculator160 relatively shifts time axes of the discharge pressure data and thereference pressure data, and calculates difference between the dischargepressure data and the reference pressure data corresponding to eachtime.

The fluctuation amount calculator 160 may set a value obtained bysumming up (integrating) the difference between the discharge pressuredata and the reference pressure data as a fluctuation amount. Also, thefluctuation amount calculator 160 may set a value obtained by summing upabsolute values of the difference between the discharge pressure dataand the reference pressure data as a fluctuation amount. If no changeoccurs to the discharge pressure data in the target detection period, orif the change is relatively small, the fluctuation amount calculated bythe fluctuation amount calculator 160 is a value no larger thandifference in integrated value of noise. For example, with respect tothe target detection period from time t_(m) to time t_(m)+T in FIG. 2,change is not occurring in the discharge pressure data to the extentthat occurrence of cavitation is recognized. That is, the differencebetween the discharge pressure data in the target detection period andthe reference pressure data from time t₀−T to time t₀ is no larger thanthe noise level.

Next, the determining unit 170 compares the fluctuation amountcalculated by the fluctuation amount calculator 160 with a referencefluctuation amount (S470). Here, the reference fluctuation amount may bepredetermined based on a fluctuation amount of the discharge pressuredata to detect. Also, the reference fluctuation amount may be no largerthan a value obtained by integrating a value of noise accepted by thedischarge pressure data by the number of times of sampling during theperiod T. For example, if a fluctuation amount is less than thereference fluctuation amount (No at S470) as shown in the targetdetection period from time t_(m) to time t_(m)+T, the detectionapparatus 100 returns to S440 and acquires the next discharge pressuredata and suction pressure data.

The discharge pressure acquiring unit 110, the suction pressureacquiring unit 120, and the detector 130 compare the fluctuation amountof the discharge pressure data in the next target period with thereference fluctuation amount in the next target period. Note that, thenext target period may be from timing back in time from a next samplingtiming of the pressure data by a period T to the sampling timing. Thatis, the next target period may be shifted from the last target period byone period of sampling timing.

Instead of this, the next target period may be shifted by N times ofperiods of sampling timing compared with the last target period (N is aninteger of two or more). In this case, at S440, the discharge pressureacquiring unit 110 and the suction pressure acquiring unit 120 acquireresults obtained by sampling the pressure data for N times. Note that,it is desirable that a period in which N times of sampling is performedis shorter than the period T.

The discharge pressure acquiring unit 110, the suction pressureacquiring unit 120, and the detector 130 repeat operation from S440 toS470 until the fluctuation amount of the discharge pressure data for thenext target period becomes the reference fluctuation amount or more (oruntil it is determined Yes at S450). Then, if the fluctuation amount ofthe discharge pressure data becomes the reference fluctuation amount ormore (Yes at S470), the determining unit 170 determines that thecavitation has occurred (S480).

For example, since change is occurring to the discharge pressure data tothe extent that occurrence of cavitation is recognized in the targetdetection period from time t_(n) to time t_(n)+T in FIG. 2, thefluctuation amount of the discharge pressure data becomes the referencefluctuation amount or more. In this case, the determining unit 170determines that cavitation has occurred, and notifies the control system70 of this fact. As described above, the fluctuation amount calculator160 according to the present embodiment uses as reference pressure data,which is the data during the normal operation of the pump 40, dischargepressure data of time length T having equal length as a target detectionperiod immediately before the timing at which the suction pressure datachanges from being a positive pressure value to a negative pressurevalue. A fluctuation amount of discharge pressure data based on suchreference pressure data and the discharge pressure data in the targetperiod will be described next.

FIG. 5 illustrates one example of a fluctuation amount of dischargepressure data calculated by a fluctuation amount calculator 160according to the present embodiment. In FIG. 5, the horizontal axisrepresents the time and the vertical axis represents the dischargepressure. FIG. 5 shows an example in which the fluctuation amountcalculator 160 relatively shifts time axes of the discharge pressuredata and reference pressure data. That is, FIG. 5 shows an example inwhich start timing and end timing of the discharge pressure data and thereference pressure data are set to time t₀₁, and time t₀₂ respectively.Note that, time t₀₂ is forward in time from time t₀₁ by time T.

Here, the fluctuation amount calculator 160 may adjust offset of thedischarge pressure data and the reference pressure data. For example,the fluctuation amount calculator 160 may relatively shift the referencepressure data to the discharge pressure data during the target detectionperiod such that a mean value of the reference pressure data matches amean value of the discharge pressure data during the target detectionperiod. Also, the fluctuation amount calculator 160 may perform afiltering processing such as a high-pass filter to remove direct currentcomponents. Additionally, the suction pressure gauge 50 and thedischarge pressure gauge 60 may supply data on which filteringprocessing has been performed.

The fluctuation amount calculator 160 may calculate, as a fluctuationamount, difference between reference pressure data and dischargepressure data during the target detection period, which have acorresponding mean value. In FIG. 5, areas illustrated with obliquelines are an example of difference between the discharge pressure dataand the reference pressure data. As shown in FIG. 5, the differencebetween the discharge pressure data and the reference pressure data mayhave difference larger than noise in an initial stage of cavitation inwhich change occurs to the discharge pressure data in the targetdetection period.

That is, by using a time waveform of the discharge pressure data, thedetection apparatus 100 according to the present embodiment can detectoccurrence of cavitation even before obvious oscillation of a certainfrequency or a frequency band occurs. Note that, pressure data acquiredfrom a plant 10 under a normal operation state may also pulse. Forexample, if liquid flowing through the pump 40 is mixture, pulsation mayoccur to the pressure data in response to the mixture ratio changing.Also, pulsation may occur to the pressure data depending onenvironmental change or the like of the plant 10. As described above, afluctuation width of certain degree of range may be seen even in thepressure data in a normal state. Therefore, by making the period of thereference pressure data approximately the same as the period T in thetarget detection period in such manner described with respect to thepresent embodiment, effect of the fluctuation width can be reduced.

Also, because the detection apparatus 100 does not perform numericalprocessing such as the Fourier transform, low cost can be achievedwithout using a complicated circuit, a high-performance CPU, or thelike. Additionally, because the detection apparatus 100 subsequentlycompares next data while erasing unnecessary previous data, storagecapacity for data can be reduced.

Note that, the detection apparatus 100 according to the presentembodiment is described with the example in which it compares timewaveforms of the reference pressure data and the discharge pressure datahaving the same time length as described in FIG. 5. However, this is notthe sole example. The detection apparatus 100 may use reference pressuredata having a time length shorter than that of the time waveform ofdischarge pressure data in the target period. In this case, thefluctuation amount calculator 160 may calculate each difference betweena mean value of the reference pressure data and individual piece of dataof discharge pressure data in the target period.

Also, the fluctuation amount calculator 160 may use as the referencepressure data one piece of discharge pressure data that is acquiredcorresponding to a timing t₀ at which the suction pressure data ischanged from being a value exceeding the threshold value to a value ofthe threshold value or less. That is, the fluctuation amount calculator160 may use as the reference pressure data the discharge pressure datathat is acquired corresponding to a timing at which the suction pressuredata changes from being a positive pressure value to a negative pressurevalue. In this case, the fluctuation amount calculator 160 may calculateeach difference between one sample of the reference pressure data andindividual piece of data of discharge pressure data in the targetperiod.

As described above, it is desirable that the detection apparatus 100uses as reference pressure data the discharge pressure data of a period,time, or the like that is closer to the timing t₀ at which the suctionpressure data changes from being a value exceeding the threshold valueto a value equal to or less than the threshold value. In this way,temporal difference between the reference pressure data and thedischarge pressure data in the target detection period can be shorter intime. That is, even if pulse occurs to pressure data, fluctuation widthsof fluctuation to occur to reference pressure data and dischargepressure data of a target detection period can be approximately thesame, and thus effect of the pulse can be reduced.

Although it is described that the above-mentioned detection apparatus100 according to the present embodiment can detect occurrence ofcavitation, it is not limited thereto. The detection apparatus 100 mayfurther predict occurrence of cavitation. Also, the detection apparatus100 may provide information about maintenance and management of the pump40. Such detection apparatus 100 will be described next.

FIG. 6 illustrates a modification example of the detection apparatus 100according to the present embodiment. With respect to the detectionapparatus 100 of the present modification example, approximately thesame operation as the operation of detection apparatus 100 according tothe present embodiment illustrated in FIG. 3 is illustrated with thesame reference numeral, and description thereof is omitted. A detector130 of the detection apparatus 100 of the present modification examplefurther has a predicting unit 210, a fluctuation amount accumulatingunit 220, and a maintenance managing unit 230.

In response to the suction pressure data becoming the threshold value orless, the predicting unit 210 predicts occurrence of cavitation of thepump 40. In this case, in response to the suction pressure data becomingthe threshold value or less, the comparator 150 notifies the fluctuationamount calculator 160 and the predicting unit 210 of the comparisonresult. The predicting unit 210 predicts occurrence of cavitation inresponse to, for example, the suction pressure data changing from beinga positive pressure value to a negative pressure value.

As described in FIG. 2, before the cavitation occurs, the suctionpressure data is gradually decreased towards a negative pressure value.Hence, the predicting unit 210 can predict cavitation to occur in thefuture depending on whether the suction pressure data has changed to thenegative pressure value. In this way, the control system 70 can performcontrol of preventing occurrence of the cavitation, preparation forperforming control on cavitation, and the like before the cavitationoccurs. Hence, not only the control system 70 can reduce occurrence ofcavitation but also rapidly handle cavitation when it occurs.

Note that, in the present embodiment, an example in which the thresholdvalue is set as a value corresponding to the atmospheric pressure isdescribed. However, this is not the sole example. Because a value ofsuction pressure data for determining a tendency of cavitation may varydepending on a type, characteristic, individual difference of the pump40, design of the control system 70, or the like, the threshold valuemay be predetermined corresponding to them. Also, different thresholdvalue may be set by the comparator 150 from a threshold value used in acase of determining whether to notify fluctuation amount calculator 160,to a threshold value used in a case of determining whether to notify thepredicting unit 210.

The fluctuation amount accumulating unit 220 calculates a cumulativevalue of a fluctuation amount of the discharge pressure data. Thefluctuation amount accumulating unit 220 may receive a fluctuationamount calculated by the fluctuation amount calculator 160 to calculatethe cumulative value. Also, the fluctuation amount accumulating unit 220may calculate the cumulative value every time cavitation occurs.Additionally, the fluctuation amount accumulating unit 220 may countfrequency of occurrence of cavitation, duration of the cavitation, orthe like. The fluctuation amount accumulating unit 220 may store theaccumulated information about the cavitation in the storage unit 140.

Based on the cumulative value of fluctuation amount of the dischargepressure data, the frequency of cavitation, the duration of thecavitation, and/or the like, the maintenance managing unit 230determines at least one of a time to maintain and time to replace thepump 40. Because the cavitation occurring in the pump 40 caused damageto the pump 40, it is considered that the cavitation affects life timeof the pump 40. Because a fluctuation amount of the discharge pressuredata corresponds to amplitude strength of oscillation of the cavitation,it can be utilized as an indicator of the damage the pump 40 hasreceived. Hence, by accumulating and recording the fluctuation amount ofthe discharge pressure data, inspection timing and replacement timing ofthe pump 40 can be determined.

The maintenance managing unit 230 may determine the inspection timingand the replacement timing of the pump 40 by, for example, comparing thecumulative value of the fluctuation amount of the discharge pressuredata with a predetermined threshold value or the like. In response tothe cumulative value becoming the threshold value or more, themaintenance managing unit 230 may notify the control system 70 of theinspection timing and/or the replacement timing. Note that, themaintenance managing unit 230 may set a different value from a thresholdvalue to determine the inspection timing to a threshold value todetermine the replacement timing. Also, the maintenance managing unit230 may predetermine the threshold value based on data regarding anactual malfunction occurred in the pump 40, life time of the pump 40,and the like.

As described above, the detection apparatus 100 according to themodification example can not only detect cavitation but also performprediction of cavitation, and maintenance and management of the pump 40at low cost. Note that, the detection apparatus 100 may only perform theprediction of cavitation or may only perform maintenance and managementof the pump 40.

With regard to the detection apparatus 100 according to the presentembodiment described above, an example in which calculation of thefluctuation amount of the discharge pressure data is started in responseto the suction pressure data becoming the threshold value or less isdescribed. In this way, the detection apparatus 100 can be preventedfrom performing calculation or the like in vain in a range in which thesuction pressure data is a normal value, and can prevent powerconsumption from increasing. Also, because the detection apparatus 100can reduce amount of calculation, even if it is implemented on thecontrol system 70, it can be prevented from affecting the control system70 as a load. Additionally, even if the detection apparatus 100 isincluded in a measuring instrument such as a sensor provided in theplant 10, it can be prevented from affecting operation thereof as aload. Furthermore, because the detection apparatus 100 does not performdetection of cavitation in a range in which the suction pressure data isa normal value, frequency of erroneous detection caused by noise or thelike can be reduced.

Note that, the detection apparatus 100 is not even limited to comparingtime waveforms, if considering such reduced power consumption andreduced frequency of the erroneous detection. For example, in responseto the suction pressure data becoming the threshold value or less, thedetection apparatus 100 may perform frequency analysis for the dischargepressure data. In this case, the fluctuation amount calculator 160 mayperform the Fourier transform on the discharge pressure data. Also, withrespect to a frequency characteristic of the discharge pressure data,the determining unit 170 may determine whether abnormality has beenoccurring in a certain wavelength or a certain band. The determiningunit 170 determines occurrence of abnormality by using, for example, apredetermined threshold value for the certain wavelength or the certainband. Accordingly, because the detection apparatus 100 starts thefrequency analysis if tendency of cavitation is seen, it can reduceamount of calculation.

Accordingly, if the detector 130 performs the frequency analysis, theoperation flow shown in FIG. 4 may be modified as follows. In S430, inresponse to the suction pressure data becoming the threshold value orless, the fluctuation amount calculator 160 sets the frequencycharacteristic of the reference pressure data. That is, the dischargepressure data acquired from time t₀−T to time t₀ is read out from thestorage unit 140 and the Fourier transform (FFT, for example) isperformed thereon to set it as the reference data.

Also, in S460, if it is determined that the tendency of cavitation iscontinuing, the fluctuation amount calculator 160 calculates a frequencycharacteristic of the discharge pressure data in the target detectionperiod. Then, the fluctuation amount calculator 160 calculatesdifference between the frequency characteristic in the target detectionperiod and the reference data on the frequency axis. Accordingly, inS470, the determining unit 170 can determine occurrence of abnormalitydepending on whether the certain wavelength or the certain band of thefrequency characteristic of difference has exceeded the threshold value.

Instead of this, the operation flow illustrated in FIG. 4 may bemodified as follows. In S460, the fluctuation amount calculator 160performs frequency conversion on waveform data indicating differencebetween reference pressure data and discharge pressure data during thetarget detection period. Accordingly, in S470, the determining unit 170can determine occurrence of abnormality depending on whether the certainwavelength or the certain band of the frequency characteristic ofdifference has exceeded the threshold value.

Although it is described that the above-mentioned detection apparatus100 according to the present embodiment detects cavitation by usingsuction pressure data and discharge pressure data, it is not limitedthereto. If in a case such as the power consumption or the like of theplant 10 is saved, such calculation for the fluctuation amount of thedischarge pressure data may continue in the range in which the suctionpressure data is a normal value. That is, the detection apparatus 100may detect cavitation by only using the discharge pressure data.

For example, the detection apparatus 100 may perform calculation for thefluctuation amount of the discharge pressure data regardless of thechange of the suction pressure data. In this case, the detectionapparatus 100 may not have the suction pressure acquiring unit 120 andthe comparator 150. In this case, the detector 130 detects occurrence ofcavitation in the pump 40 based on a fluctuation amount of dischargepressure data during a target detection period. The detector 130 uses asreference pressure data the discharge pressure data acquired in a casein which operation of the pump 40 and/or the detection apparatus 100 isstarted, for example.

Also, the detector 130 may use as the reference pressure data thedischarge pressure data acquired in a case in which the pump 40 isperforming normal operation in advance. Also, the detector 130 may useas the reference pressure data a predetermined value such as a designvalue, an empirical value, or the like.

Accordingly, if the detection apparatus 100 performs calculation for thefluctuation amount of the discharge pressure data regardless of thechange of the suction pressure data, the operation flow shown in FIG. 4may be modified as follows. That is, operation in S420 and S450regarding the suction pressure data are not performed. Also, withrespect to the acquiring of the pressure data in S410 and S440, it maybe sufficient if the discharge pressure acquiring unit 110 acquires thedischarge pressure data. In this way, based on a time waveform of thedischarge pressure data, the detection apparatus 100 can detectoccurrence of cavitation.

Accordingly, the detector 130 may detect occurrence of cavitation in thepump based on difference between discharge pressure data during a targetdetection period and discharge pressure data before the target detectionperiod.

Note that, in this case, the detector 130 may detect occurrence ofcavitation in the pump based on, for example, difference betweendischarge pressure data during a target detection period and dischargepressure data immediately before the target detection period.

Because the fluctuation amount of the discharge pressure data graduallyincreases and gets worse after occurrence of cavitation, the detectionapparatus 100 can detect the occurrence of cavitation by comparingtemporally preceding discharge pressure data with temporally succeedingdischarge pressure data. In this case, the operation flow illustrated inFIG. 4 may be further modified as follows. That is, in S470, if thefluctuation amount is less than the reference fluctuation amount (No atS470), return to S430 instead of S440, and set the discharge pressuredata in the target period as the reference pressure data. Then, thedischarge pressure data for the next target period is acquired (S440).

In this way, the detection apparatus 100 can compare the temporallypreceding discharge pressure data with the temporally succeedingdischarge pressure data without using the suction pressure data, and candetect occurrence of cavitation. That is, the detection apparatus 100can detect occurrence of cavitation while having simpler configuration.Also, the detection apparatus 100 can detect change in real timecavitation.

Note that, if considering the detection of such change in real timecavitation, the detection apparatus 100 is not limited to detectingoccurrence of cavitation by comparing the difference of time waveformswith the reference fluctuation amount. For example, the detectionapparatus 100 may detect cavitation by performing frequency conversionon the difference between discharge pressure data during the targetdetection period and the discharge pressure data before the targetdetection period.

In this case, the fluctuation amount calculator 160 may calculate thedifference between the discharge pressure data in the target detectionperiod and the reference pressure data before performing the Fouriertransform on the difference. With respect to a frequency characteristiccalculated by the fluctuation amount calculator 160, the determiningunit 170 may determine whether abnormality has been occurring in acertain wavelength or a certain band. The determining unit 170determines occurrence of abnormality by using, for example, apredetermined threshold value for the certain wavelength or the certainband. This operation can be realized by further modifying S460 and S470.

With respect to the detection apparatus 100 according to the presentembodiment described above, an example in which the pressure data isacquired from a pressure gauge such as the suction pressure gauge 50 andthe discharge pressure gauge 60 is described. In addition to this, thedetection apparatus 100 may also acquire fault information or the likeof the pressure gauge from the suction pressure gauge 50 and/or thedischarge pressure gauge 60. If a malfunction or the like is occurringto the pressure gauge, it is difficult to accurately detect occurrenceof cavitation. Thus, if fault information or the like for the pressuregauge is acquired, the detection apparatus 100 may not perform thedetection of cavitation. Instead of this, the detection apparatus 100may add the fault information to a detection result of cavitation andnotify the control system 70.

An example in which the detection apparatus 100 according to the presentembodiment described above is provided to the plant 10 is described.Note that, the plant 10 is an example of a system utilizing the pump 40to transfer liquid. The system to which the detection apparatus 100 isprovided is not limited to the plant 10. Cavitation may occur to a pump40 as long as it is for transferring liquid. Thus, the cavitation may bedetected by providing the detection apparatus 100 to a system, anapparatus, or equipment using the pump 40, or the site or the like ofuse of the pump 40.

FIG. 7 illustrates an exemplary configuration of a computer 1200 inwhich a plurality of aspects of the present invention may be fully orpartially embodied. A program installed in the computer 1200 can makethe computer 1200 function as an operation which is associated with theapparatus according to the embodiment of the present invention, or oneor more “unit(s)” of the apparatus, or can make the computer 1200perform the operation or the one or more “unit(s)”, and/or can make thecomputer 1200 perform processes according to the embodiment of thepresent invention or steps of the processes. Such programs may beexecuted by a CPU 1212 so that the computer 1200 performs particularoperations associated with some or all of blocks in the flowchart andthe block diagrams according to the present specification.

The computer 1200 according to the present embodiment includes a CPU1212, a RAM 1214, a graphics controller 1216, and a display device 1218,and these are connected to each other by a host controller 1210. Thecomputer 1200 also includes input/output units such as a communicationinterface 1222, a hard disk drive 1224, a DVD-ROM drive 1226 and an ICcard drive, which are connected to the host controller 1210 via aninput/output controller 1220. The computer also includes legacyinput/output units such as a ROM 1230 and a keyboard 1242, these areconnected to the input/output controller 1220 via an input/output chip1240.

The CPU 1212 operates according to programs stored in the ROM 1230 andthe RAM 1214, and thereby controls each unit. The graphics controller1216 acquires image data generated by the CPU 1212 on a frame buffer orthe like provided in the RAM 1214 or in the graphics controller 1216itself, and makes the image data to be displayed on the display device1218.

The communication interface 1222 communicates with other electronicdevices via a network. The hard disk drive 1224 stores programs and dataused by the CPU 1212 within the computer 1200. The DVD-ROM drive 1226reads the programs or the data from the DVD-ROM 1201, and provides thehard disk drive 1224 with the programs or the data via the RAM 1214. TheIC card drive reads programs and data from the IC card, and/or writesprograms and data into the IC card.

The ROM 1230 stores therein a boot program etc. executed by the computer1200 at the time of activation, and/or a program that depend on thehardware of the computer 1200. The input/output chip 1240 may alsoconnect various input/output units to the input/output controller 1220via a parallel port, a serial port, a keyboard port, a mouse port etc.

A program is provided by computer readable storage medium such as theDVD-ROM 1201 or the IC card. The program is read out from the computerreadable storage medium, installed into the hard disk drive 1224, RAM1214 or ROM 1230, which are also examples of computer readable storagemedium, and executed by the CPU 1212. The information processingdescribed in these programs is read out by the computer 1200, resultingin cooperation between a program and the above-mentioned various typesof hardware resources. An apparatus or method may be constituted byrealizing the operation or processing of information, according to theusage of the computer 1200.

For example, when communication is performed between the computer 1200and an external device, the CPU 1212 may execute a communication programloaded onto the RAM 1214 to instruct communication processing to thecommunication interface 1222, based on the processing described in thecommunication program. The communication interface 1222, under controlof the CPU 1212, reads transmission data stored on a transmissionbuffering region provided in a recording medium such as the RAM 1214,the hard disk drive 1224, the DVD-ROM 1201, or the IC card, andtransmits the read transmission data to a network or writes receptiondata received from a network to a reception buffering region or the likeprovided on the recording medium.

Additionally, the CPU 1212 may cause all or a necessary portion of afile or a database to be read into the RAM 1214, the file or thedatabase having been stored in an external recording medium such as thehard disk drive 1224, the DVD-ROM drive 1226 (DVD-ROM 1201), the ICcard, etc., and perform various types of processing on the data on theRAM 1214. The CPU 1212 may then write back the processed data to theexternal recording medium.

Various types of information, such as various types of programs, data,tables, and databases may be stored in the recording medium forinformation processing. The CPU 1212 may perform, on the read-out datafrom the RAM 1214, various types of processing which includes varioustypes of operations, information processing; conditional judging,conditional branch, unconditional branch, information search/replaceetc., as described throughout the present disclosure and designated byan instruction sequence of the program, and write backs the result tothe RAM 1214. Also, the CPU 1212 may search for information in a file, adatabase etc. in the recording medium. For example, when a plurality ofentries, each of them having an attribute value of a first attributeassociated with an attribute value of a second attribute are stored inthe recording medium, the CPU 1212 may search for, from among theplurality of entries, an entry where the attribute value of the firstattribute matches a designated condition, may read the attribute valueof the second attribute stored in the entry, and thereby may acquire theattribute value of the second attribute associated with the firstattribute that satisfies a predetermined condition.

The above-explained program or software modules may be stored in thecomputer readable storage medium on or near the computer 1200. Also, arecording medium such as a hard disk or a RAM provided in a serversystem connected to a dedicated communication network or the Internetcan be used as the computer readable storage media, and thereby providethe programs to the computer 1200 via network.

While the embodiments of the present invention have been described, thetechnical scope of the invention is not limited to the above describedembodiments. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiments. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

What is claimed is:
 1. A detection apparatus comprising: a dischargepressure acquiring unit to acquire discharge pressure data indicatingdischarge pressure of a pump; and a detector to detect occurrence ofcavitation in the pump based on a fluctuation amount of a time waveformof the discharge pressure data during a target detection period.
 2. Thedetection apparatus according to claim 1, wherein the detector has: afluctuation amount calculator to calculate the fluctuation amount of thedischarge pressure data during the target detection period; and adetermining unit to determine that cavitation has occurred in the pump,in response to the calculated fluctuation amount becoming referencefluctuation amount or more.
 3. The detection apparatus according toclaim 2, wherein the fluctuation amount calculator calculates, as thefluctuation amount, difference between reference pressure data and thedischarge pressure data during the target detection period.
 4. Thedetection apparatus according to claim 3, wherein the fluctuation amountcalculator calculates the difference between the discharge pressure dataduring the target detection period and the reference pressure data for atime length equal to the target detection period as the fluctuationamount.
 5. The detection apparatus according to claim 3, wherein thefluctuation amount calculator uses the discharge pressure data that isacquired by the discharge pressure acquiring unit before the targetdetection period as the reference pressure data.
 6. The detectionapparatus according to claim 5, further comprising: a suction pressureacquiring unit to acquire suction pressure data showing suction pressureof the pump, wherein the fluctuation amount calculator uses as thereference pressure data the discharge pressure data acquiredcorresponding to timing at which the suction pressure data changes froma value exceeding a threshold value to a value equal to or less than thethreshold value.
 7. The detection apparatus according to claim 6,wherein the fluctuation amount calculator uses the discharge pressuredata that is acquired corresponding to a timing at which the suctionpressure data changes from being a positive pressure value to a negativepressure value as the reference pressure data.
 8. The detectionapparatus according to claim 6, wherein the fluctuation amountcalculator uses discharge pressure data for a time length equal to thetarget detection period immediately before the timing as the referencepressure data.
 9. The detection apparatus according to claim 3, whereinthe fluctuation amount calculator is to, relatively shift the referencepressure data to the discharge pressure data during the target detectionperiod, and match a mean value of the reference pressure data with amean value of the discharge pressure data during the target detectionperiod, and calculate, as the fluctuation amount, difference between thedischarge pressure data and the reference pressure data during thetarget detection period, of which mean values are matched.
 10. Thedetection apparatus according to claim 1, further comprising: afluctuation amount accumulating unit to calculate a cumulative value ofthe fluctuation amount; and a maintenance managing unit to determine atleast one of time to maintain and time to replace the pump based on thecumulative value of the fluctuation amount.
 11. A detection apparatuscomprising: a suction pressure acquiring unit to acquire suctionpressure data indicating suction pressure of a pump; a dischargepressure acquiring unit to acquire discharge pressure data indicatingdischarge pressure of the pump; and a detector to detect whethercavitation is occurring in the pump based on the discharge pressure datain response to the suction pressure data becoming a threshold value orless.
 12. The detection apparatus according to claim 11, furthercomprising: a predicting unit to predict occurrence of cavitation in thepump in response to the suction pressure data becoming the thresholdvalue or less.
 13. A detection apparatus comprising: a dischargepressure acquiring unit to acquire discharge pressure data indicatingdischarge pressure of a pump; and a detector to detect occurrence ofcavitation in the pump based on difference between the dischargepressure data during a target detection period and the dischargepressure data before the target detection period.
 14. A detection methodcomprising: acquiring discharge pressure data indicating dischargepressure of a pump; and detecting occurrence of cavitation in the pumpbased on a fluctuation amount of a time waveform of the dischargepressure data during a target detection period.
 15. A computer readablemedium to store a program, the program causing a computer to serve as: adischarge pressure acquiring unit to acquire discharge pressure dataindicating discharge pressure of a pump; and a detector to detectoccurrence of cavitation in the pump based on a fluctuation amount of atime waveform of the discharge pressure data during a target detectionperiod.
 16. A detection method comprising: acquiring suction pressuredata indicating suction pressure of a pump; acquiring discharge pressuredata indicating discharge pressure of the pump; and detecting whethercavitation is occurring in the pump based on the discharge pressure datain response to the suction pressure data becoming a threshold value orless.
 17. A computer readable medium to store a program, the programcausing a computer to serve as: a suction pressure acquiring unit toacquire suction pressure data indicating suction pressure of a pump; adischarge pressure acquiring unit to acquire discharge pressure dataindicating discharge pressure of the pump; and a detector to detectwhether cavitation is occurring in the pump based on the dischargepressure data in response to the suction pressure data becoming athreshold value or less.
 18. A detection method comprising: acquiringdischarge pressure data indicating discharge pressure of a pump; anddetecting occurrence of cavitation in the pump based on differencebetween the discharge pressure data during a target detection period andthe discharge pressure data before the target detection period.
 19. Acomputer readable medium to store a program, the program causing acomputer to serve as: a discharge pressure acquiring unit to acquiredischarge pressure data indicating discharge pressure of a pump; and adetector to detect occurrence of cavitation in the pump based ondifference between the discharge pressure data during a target detectionperiod and the discharge pressure data before the target detectionperiod.